Gas tank fuel systems with reduced gasoline vapor loss are becoming increasingly important in the automobile industry to reduce needless loss of fuel. The typical solution to this problem has been to reduce the diameter of at least a section of the fuel tank filler neck. Though this approach has been somewhat successful, it is limited because as the diameter of the filler neck is decreased, the resistance to flow of the gasoline is increased. The increased resistance causes the fill neck to become filled during vehicle refueling thereby blocking release of any pressure buildup and causing the fuel nozzle to shut off prematurely before the fuel tank is full.
Another disadvantage of such methods of reducing gasoline vapor losses is that typically the end of the gas line filler neck is flared out in order to provide a sufficient diameter to accept the gas nozzle during refueling. Since the fuel tank filler neck is usually fabricated from butt-seam welded tubing, there is an increasing tendency for the integrity of the weld to leak as thinner diameter tubes are utilized.